1. Field of the Invention
The present invention relates to a device for performing surgery on the cornea of the eye.
2. Discussion of Prior Art
The purpose of such modifications of the shape of the cornea is to correct ametropia by correcting dimensional optical characteristics of the cornea and principally its radius of curvature. At the present time such modifications, known as keratomileusis, are achieved by actually machining a disk removed from the cornea. The disk is made rigid by freezing it and then machined by the Barraquer process or applied to a template with the appropriate radius of curvature and recut using the Barraquer-Krumeich technique.
This type of operation has the major disadvantage of necessitating first removal of the disk of corneal material and then treatment of the aforementioned disk, which has to be reimplanted on the eyeball of the patient after treatment.
However, recent work has shown the very precise ablative properties of excimer laser radiation when this radiation is applied to the corneal tissue. The radiation emitted by an excimer laser, with a wavelength substantially equal to 193 nm, may be used to eliminate corneal material by photodecomposition. Generally speaking, a round light spot (an image of the laser beam) is formed on the cornea, the spot being substantially centered on the optical axis of the eyeball. The spot has a substantially circular or annular shape or a symmetrical shape relative to the optical axis of the eyeball and may be moved and/or the radius/size changed, the exposure time for a particular area depending on the thickness of the cornea to be eliminated.
Although such devices enable direct operation on the eyeball of the patient, enabling better centering through avoiding the aforementioned problem of cutting out, and reimplanting after correction, a piece of the cornea, they do not make it possible to implement a precise treatment method in that, although the exposure time can be defined with good precision, the effects and in particular the thickness of the cornea subjected to photodecomposition vary with the size of the light spot and the energy density of the laser beam used. Moreover, the surface state of the cornea after treatment and undesirable side effects due to thermal or shockwave phenomena vary significantly with the energy level delivered by each pulse and the repetition frequency with which the same area is successively irradiated.